drm/i915: split gem quirks from display quirks

The lone gem quirk is an outlier, not even handled by the common quirk
code. Split it to a separate gem_quirks member.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/fe9c0cb1e49da0ddc31d24c996af5fd09bce3042.1661346845.git.jani.nikula@intel.com